The Constraints Editor is a Graphical User Interface (GUI) that can be used after you run the NGDBUILD program to create new constraints. It runs on Windows NT/95 and on workstations.
The Constraints Editor interface consists of a main window, three tab windows and a number of dialog boxes. A brief description of the windows is included below. Window and dialog box functionality is described in the “Windows and Dialog Boxes” chapter.
The main window is used to load files, to access the tab windows, and to view editable and read-only constraints.
Figure 1.1 Constraints Editor Main Window |  |
For more about the main window, see the “Main Window” section in the "Windows and Dialog Boxes" chapter.
The Global tab window shows a table of all of the design's clock nets and the associated period, pad-to-setup, and clock-to-pad values. It also contains a field for displaying a global pad-to-pad value.The Global tab window is the default window displayed when a file is loaded into the Constraints Editor.
Figure 1.2 Global Tab Window | |
For more about the Global tab window, see the “Global Tab Window” section in the "Windows and Dialog Boxes" chapter.
The Ports tab window displays a table of all current ports and a list of currently unused pad names in the design, allowing you to lock any port to a specified package pin, to enter any clock-specific constraint, and to indicate the configuration of an I/O in terms of fast or slow slew rate (transition time of the signal).
Figure 1.3 Ports Tab Window | |
For more about the Ports tab window see the “Ports Tab Window” section in the "Windows and Dialog Boxes" chapter.
The Advanced tab window contains a number of fields for creating new constraints and for displaying and managing editable and read-only constraints.
Figure 1.4 Advanced Tab Window | |
For more about the Advanced tab window see the “Advanced Tab Window” section in the "Windows and Dialog Boxes" chapter.
The details of the constraints language are displayed in the Constraints window (see the figure below).These constraints are displayed in two groups: those that can be edited and those that are read-only.
By default, the Constraints window is open when you open an NGD file.To hide the window, click the right mouse button 
click Hide. To make the window reappear, click Window on the menu bar click Constraints Window.
Figure 1.5 Constraints Window | |
The software accepts NGD (Native Generic Database) and an optional UCF (User Constraint File) files as inputs. It outputs UCF files. The output files contain the changes made in the Constraints Editor.
By default, when the NGD file is opened, an existing UCF file with the same base name as the NGD file will be used. Alternatively, you can specify the name of the UCF file.
Upon successful completion, the Constraints Editor writes out a valid UCF file. NGDBuild uses a UCF, along with design source netlists, to produce an NGD file. The NGD file is read by the MAP program, which generates an NCD (Native Circuit Description) file, which is a physical design database, and a PCF (Physical Constraints File). The implementation tools use the NCD and PCF files to produce a bitstream.
Figure 1.6 Constraints Editor Flow | |
In this software release, not all Xilinx constraints are accessible through this GUI. Constraints supported in the GUI and the associated UCF syntax are described in the “UCF Syntax” appendix.
